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Sunday, July 31, 2011

The first time I encountered a black widow was in the desert of eastern Oregon. I cannot recall the circumstances exactly, but I was rather awed, given that I had read about them but never seen one until then. Thanks to the book How to Know the Spiders, by B. J. Kaston, I learned the species found in the Pacific Northwest is the Western Black Widow, Latrodectus hesperus.

Eventually, I was able to easily identify black widow webs, even if the spider was not present. Black widow webs are large, three dimensional tangles of extremely strong threads. The whole web can easily occupy a cubic foot or more, and you can pluck the silken strands like guitar strings without them breaking. A funnel-like retreat is usually seen going into a rodent burrow, under a boulder, or some other cavity that would take heavy machinery to break into. Black widows do not want anything to do with larger animals. Only at night are you likely to see the spider out on her web.

Believe it or not, black widows begin their lives as largely *white* spiders. They lose the pale spots and stripes as they age, but because males mature more quickly, in fewer molts, they never lose their pale markings entirely. Even the immature spiders sport at least some semblance of an “hourglass” marking on the underside of their abdomen, so you can still identify them as widows. Since widows sit upside down in their webs, that hourglass marking is usually visible.

The Western Black Widow is the largest North American member of the genus Latrodectus. Females have a body length of 14-16 millimeters as adults, males 7-8 millimeters. Mature females usually lack any red markings besides the hourglass, and that may be broken or even wanting in some specimens. Some individuals may be chocolate brown instead of black.

Mature males are recognized by their swollen pedipalps, which resemble tiny boxing gloves located near the spider’s face. He uses these as intromittent sex organs that fit like a key in the “lock” of the female’s paired genital openings. Contrary to popular myth, the female does not always cannibalize her mate, though sex is a risky business for nearly all male spiders.

Mated females can produce several egg sacs in their lifetime, each containing up to 750 eggs. Few of the spiderlings that emerge will make it to maturity themselves, due to cannibalization by siblings and other natural hazards. Adult females can live more than a year, though.

Western Black Widows are able to secure surprisingly large prey. Their webs are designed to trap prey walking over the ground. When a victim stumbles into one of the sticky trip threads attached to the ground, the thread breaks and rebounds, yanking the potential prey animal into the main body of the web. The trip threads are so elastic and strong that even small vertebrates can be captured in widow webs. I personally witnessed a hatchling lizard struggling in a web. Yes, I intervened.

While black widows have no problem killing prey as imposing as large beetles, they flee rapidly when they sense a larger creature such as a human. The speed at which they can scramble back into their retreat is astonishing. I have had many a photo opportunity cut short when I accidentally bumped a thread.

The Western Black Widow is a very common spider found from extreme southern British Columbia south to Mexico and west to Kansas, Oklahoma, and Texas. It is particularly abundant in drier habitats such as deserts and prairies, though it can be encountered in more damp situations as well.

Because of the timid nature of widows, it is relatively easy to minimize the possibility of being bitten. Simply take these precautions:

Never leave clothing, shoes, or gloves outdoors overnight. A spider can seek shelter during that time.

Do not put your hands or feet where you cannot see into, such as holes and crevices, inside the mailbox, or behind large objects that have been in storage for awhile.

Carefully inspect firewood, houseplants, toys, etc being brought indoors from outside in case a spider may be hitchhiking on the object.

Do not walk barefoot outdoors, especially at night.

Reactions to bites from widows can vary considerably from one person to the next because immune system responses to envenomation are highly individualistic. The spider may not even deliver much, if any, venom. Still, they typical experience is excruciating. The venom is neurotoxic, meaning it affects the nervous system. This translates to triggering constant muscle contractions that result in severe cramps, especially in the abdomen, legs, and other large muscle groups. One friend of mine had back spasms for months following a black widow bite. One should always seek emergency hospitalization immediately, precisely because one cannot be sure how their body will react. Antivenin is available for treatment, though it is recommended as a last resort by most hospital physicians. Antivenin is produced from horse serum, which can carry its own complications including allergic reactions. Obviously, avoiding bites is preferable to treating them after the fact.

Black widows cannot be easily “controlled.” Contact insecticides have a very low probability of reaching a hidden spider, and killing one spider means it will soon be replaced by another anyway (prime web sites are a coveted commodity). Meanwhile, the spiders will kill plenty of pest insects that could potentially be more trouble than the spiders themselves. By all means, do inspect playground equipment and toys before allowing your children to play outdoors. It all comes back to vigilance and prevention. Take care, but value the work your spiders do.

Friday, July 29, 2011

The other day I came out of my apartment to find a piece of paper stuck in my screen door. I was dreading reading about a rent increase, but the announcement was unpleasant in a different way. “We are starting a new program here at (name of apartment complex)” began the notice. Turns out that the management is initiating an ongoing pest control schedule, no doubt due to someone complaining about German Cockroaches, Blattella germanica.

I have had German roaches in my own apartment previously. Initially I did not treat for them because a Mediterranean House Gecko, Hemidactylus turcicus, had also taken up residence in my kitchen and kept the roach population to tolerable levels. Eventually, the lizard died, and then the roach population exceeded my psychological and physical “carrying capacity.”

I reluctantly purchased some roach bait traps, and that did the trick….until a few months ago, when I saw another roach. In the last month I have killed two: a male and a female. Still, I have a hard time with the invasion of privacy that comes with an extermination service, not to mention having some trepidation over whatever chemical treatment they are applying.

Ok, enough about me, how about some background on the German Cockroach? It is believed that most of our “domiciliary” roach species are native to tropical Africa, and can only exist outside their normal geographic range by occupying buildings that offer a year-round approximation of their tropical homeland. Why are they called “German,” then? Well, here in the United States at least, we have a history of naming economic pests after nationalities that we have had conflicts with. So, given our World War II enemies, it seemed fitting to apply the “German” epithet to this particular roach species (in Germany the species is called the “Russian” Cockroach).

The German Cockroach is one of the smaller roach species, ranging from 11-13 millimeters in length. Consequently, it is sometimes mistaken for some other kind of insect and dismissed. There is no ignoring their numbers, however, and opening a cupboard can send dozens of them scurrying for darkness in a dwelling that is infested with them. Males are sleek, slender, amber-colored insects, while females tend to be darker and more robust. Both genders are shown in the images here. See if you can tell which is which.

As far as I am aware, domestic pest roaches have only been implicated in the mechanical transmission of bacteria, never actually proven to be carriers of Salmonella and other treacherous microbes. Roaches groom themselves constantly, lest they themselves become victims of pathogens and fungi. This is not to say that cockroaches are at worst a nuisance. Far from it.

What has been conclusively demonstrated is that cockroach body parts, shed exoskeletons (remember roaches have to molt to grow), and fecal matter are a major, major trigger of asthma, especially in children. This is one reason that neglect of public housing should be a crime: improper maintenance can lead to chronic health issues that are far more costly to society (and the individual) in the long run. Also, entomologists who study roaches in the lab frequently develop allergies to roach exoskeletons, feces, and body parts. Such afflictions are sometimes severe enough to cause the scientists to abandon roaches as study subjects.

Cockroaches are successful organisms for several reasons. They achieved near perfection in the evolutionary sense millions of years ago, judging by the fossil record of roaches that are essentially identical to contemporary species. They are generalist feeders, able exploit all manner of organic matter. They are adept at detecting and avoiding poisons, being able to taste-test food before ingesting any. They reproduce at a rate that makes rabbits envious.

Female German Cockroaches cannot be accused of parental neglect. Once mated, a female will produce an egg capsule called an “ootheca.” Each ootheca contains an average of 30-40 eggs. The female carries the capsule at the tip of her abdomen until just before the eggs are ready to hatch. Then she carefully deposits the egg case in a crack or crevice where the cockroach nymphs can emerge in relative safety. Each female roach can produce several ootheca during her lifetime.

A typical roach population is a youthful one, comprised of about eighty percent nymphs of various stages and twenty percent adults. I haven’t seen any nymphs in my home lately, and I hope it stays that way.

Wednesday, July 27, 2011

I can always count on an aphid-infested tree to provide me endless hours of enjoyment. Aphids secrete a sweet, liquid waste product called “honeydew.” This substance attracts an enormous diversity of wasps, bees, flies, and other insects (even butterflies). I found just such a tree, a young aspen, at the Cheyenne Mountain Zoo in Colorado Springs, Colorado last week. Among the numerous hymenopterans seeking refreshment was a mason wasp that goes by the unfortunately long name of Ancistrocerus tuberculocephalus.

Mason wasps are solitary members of the family Vespidae, which includes familiar social species like yellowjackets and paper wasps. Nearly all members of that family fold their wings longitudinally when at rest, so that behavior is often a good way to identify them.

While some of the mason wasps make free-standing nests of mud, the majority nest in pre-existing cavities, partitioning the interior space into separate cells.

Ancistrocerus tuberculocephalus is known to use the abandoned mud nests of the Black and Yellow Mud Dauber, Sceliphron caementarium, for its own nests. It can also dig out the pith in sumac twigs and nest inside the resulting hollow; or it can use old beetle borings in dead wood. The female wasp provisions each cell with paralyzed caterpillars that will be the food source for the single larva that develops in each cell.

This species is divided into two subspecies. A. tuberculocephalus sutterianus ranges from British Columbia to California, Nevada, and Utah. Below is a specimen of this subspecies from near Long Beach, California.A. tuberculocephalus tuberculocephalus occurs from South Dakota and Wyoming to Utah, Colorado, Arizona, New Mexico, and west Texas. The remaining images in this post are of specimens from Colorado Springs.

You can help provide housing for these flying pest control agents by simply leaving old mud dauber nests where they are. Should you be feeling more industrious, consider bundling old sumac twigs and hanging them under an eave;or drill six-inch holes of various diameters into a block of wood and tack it up.Many solitary wasps, and bees, too, need the extra real estate these days as their habitats disappear amid suburban sprawl. The wasps won’t bother you, and you might make some interesting discoveries about them.

Special thanks to David R. Green for use of his image of the twig trap nest, complete with a solitary wasp peering out of it. Thanks also to "Birds n' Such" for the image of the upscale bee block.

Sunday, July 24, 2011

While living in Massachusetts in 2009 I had the pleasure of prowling around some very nice natural areas with Lynn Harper, an accomplished naturalist who works for the Natural Heritage and Endangered Species Program in the Massachusetts Division of Fisheries and Wildlife. Among the places I went with Lynn was Tully Lake in Royalston. There I was to encounter a very large wolf spider in a wet meadow near the lake.

Scientists have not made it a priority to assign common (English) names to individual species of insects and spiders, unless the creature is of economic significance. Consequently, there is no specific name for this magnificent, eye-catching arachnid. It is probably the species Hogna helluo, though without a thorough physical exam of the specimen it is nearly impossible to be certain. Spiders darken with age, and there is plenty of variability in color and pattern from individual to individual anyway.

Wolf spiders comprise the family Lycosidae, and most of the large North American species belong to the genus Hogna. They used to be classified in the genus Lycosa, but a revision of that genus resulted in the finding that there are no New World species in the genus Lycosa. North American species were thus reassigned to Hogna.

Arachnologists measure spiders by body length, not legspan, but even by that standard, Hogna are real giants. Mature males of H. helluo range from 10-12 mm, while females are a whopping 18-21 mm. Add the sprawling legs and they are an intimidating creature to those unfamiliar with their skittish nature.

Wolf spiders in general hunt “on foot” instead of building webs to snare their prey. Consequently they are more muscular than the average arachnid, with keen eyesight. They are most active at night, perhaps because their arch enemies the spider wasps (family Pompilidae) hunt during the day. Try hunting for wolf spiders yourself, at night. Shine a flashlight or a headlamp over a field, or even a lawn, and you will see the eyes of wolf spiders sparkling like diamonds as they reflect the beam of your light.

Wolf spiders can simply overpower their prey, and if you witness one attacking a cricket or other insect you will probably be shocked by the violence. Still, a wolf spider is going to flee at top speed from your approach. I was fortunate to reel off a number of pictures before this female fled among the grass and moss.

There are many stories to tell about wolf spiders, so I will give away no more secrets today. I will simply encourage you to go out and look for them yourself; and ask that you treat the odd wolf spider that enters your home with a little respect. Please relocate such spiders back outdoors where they can intercept invading insects that could do you, your family and pets real harm. Thank you.

Wednesday, July 20, 2011

When it comes to mimicry of wasps, the flower flies of the family Syrphidae are perhaps unequaled. They are convincing enough that I myself remain prone to being fooled by some of these imposters. Among the best of the best are members of the genus Spilomyia, which not only look like yellowjackets, but even sound like them.

A recent trip to Colorado Springs, Colorado revealed just how easy it is to pull the wool over my eyes. At the Cheyenne Mountain Zoo I had been seeing both Aerial Yellowjackets (Dolichovespula arenaria) and Western Yellowjackets (Vespula pensylvanica) licking aphid honeydew off of leaves on a young aspen tree. One of the “yellowjackets” didn’t look quite right, though, and a closer inspection revealed it to be a fly.

One way I am able to tell flower flies from yellowjackets is by the antennae. Yellowjackets have long, thick antennae, whereas most of the flies have very short antennae with a hair-like appendage called an arista on the very tip. Some flower flies, including those in the genus Spilomyia compensate for this difference by waving their front legs in front of their faces to simulate the longer, thicker antennae of the wasps.

Fine. I can always tell the difference by the eyes. Flies have very large eyes that meet at (males) or near (females) the top of their heads. This should be easy. Ok, wait a minute, exactly where do this fly’s eyes end and the rest of its face begin? Swell. The ornate black and yellow markings on the fly’s eyes now make sense: they break up the outline of the eyes, making them appear smaller than they actually are.

Alright, I don’t give up that easily. Flies have only one pair of wings, while wasps have two. Ha! I got you now. Also, the wings of yellowjackets are folded longitudinally when the wasp is at rest, so the wings appear thinner and darker….Uh oh. This fly actually has the front half of each wing darkened to mimic that fold. Unreal.

The flies are also the same size as yellowjackets, varying from 12-17 millimeters in body length. But, as if visual appearance and behavior are not enough to convince a would-be predator not to mess with the fly, this mimic even sounds like a wasp. The frequency of its wingbeats in flight is nearly identical to that of its yellowjacket model. One has to wonder if any predator or parasite can see (and hear) through this charade.

Flower flies are more than just a pretty face, though. The adults visit flowers, and they can be at least adequate pollinators as a result of this behavior. The larval stages of Spilomyia apparently dwell inside water-filled tree holes, feeding on decaying organic matter. So, they are valuable recyclers and decomposers, too.

The next time you think you see a yellowjacket in your yard or garden, do a double-take; maybe a triple-take. You might just be seeing a fly in disguise. Spilomyia is a very widespread genus with about 13 species in North America, so chances are good that they are in your neighborhood.

Sunday, July 17, 2011

Among my most favorite spiders are the fishing spiders in the genus Dolomedes, family Pisauridae. They are elegant ambush hunters, and perhaps none more so than the Six-spotted Fishing Spider, Dolomedes triton. This species is widespread in North America, but not seen that frequently, being especially scarce in the Midwest and Rocky Mountains.

These are not small spiders, mature females attaining a body length of 17-20 millimeters, and males 9-13 millimeters. Their extensive legspan makes them appear larger still. They can vary considerably in color and pattern from one individual specimen to another, but the “standard” form sports two rows of white spots on the abdomen. They don’t always add up to the spider’s namesake six, though.

Fishing spiders are famed for their feats of predatory strength in killing small fish, tadpoles, and frogs. Indeed, D. triton is capable of preying on aquatic vertebrates four to five times the spider’s own weight. The spider reacts to the concentric waves created by a surfacing organism. The spider cannot see well, but its sense of touch more than makes up for any visual deficiency. It is able to pinpoint the epicenter of waves with extraordinary precision, and strike with lightning speed. Still, it rarely goes after large prey, and succeeds less than 10% of the time (unless the prey item actually bumps into the spider, in which case the success rate increases to 16%). Most items on the spider’s menu are terrestrial or aerial insects that get blown onto the water’s surface, or fall from overhanging vegetation.

D. triton can pursue prey underwater, but that is a rare behavior. It is more likely to dive to avoid its own predators, namely the spider wasp Anoplius depressipes. Fine hairs covering the spider’s body trap a layer of air against its breathing holes when the spider goes under. Again, this is usually a last ditch attempt at escape when all else fails.

The spider normally rests motionless on emergent vegetation or floating objects in the quiet water of a pond, lake, or river backwater, maintaining contact with the water surface with the first two pair of legs. This is not to say that the spider can’t propel itself across the surface of the water if it wants to. It can, in fact, do so passively or actively, and slowly or rapidly.

Fishing spiders can raise their front pair of legs into the wind and be blown by the most imperceptible of breezes. This form of locomotion is called “sailing,” and the spider has little control over its speed. The most common form of movement over the water executed by Dolomedes is called “rowing.” The spider actually makes the water surface itself do the work. The tip of each leg creates a dimple on the water surface, and by stroking the third and second pair of legs backwards (in that order), the dimples act as oars, pushing water toward the rear of the spider and moving it forward. This is a rather leisurely mode and speed of travel.

When a fishing spider wants to flee a predator or pursue fast prey, it can shift to “gallop” speed. In this case, the spider abandons the dimple propulsion strategy and simply slices the water rapidly with the tips of its legs. Its body is elevated above the surface when galloping, and at certain points the animal is completely airborne. This method of locomotion can result in astonishing maximum speeds of three feet per second. The spider cannot sustain that velocity for very long, however.

Male D. triton spiders have the unenviable task of convincing females that they are not an appetizer. So, they may initiate courtship by literally being “jerks,” using their legs to generate an unmistakable series of rhythmic surface waves that contact the female spider. Alternatively, he may follow the female’s silken dragline, then engaging in rapid leg-tapping as he approaches her more closely. The two spiders touch legs in an apparent identity-verification dance.

Mated females create a spherical egg sac that they cart around in their jaws and pedipalps until just before the spiderlings are likely to hatch. At that point the mother spider spins a “nursery web” and suspends the egg sac inside. She will then guard the egg sac, and the spiderlings that hatch from it. Once the spiderlings molt again, they will disperse and the female will resume her normal hunting lifestyle.

Wednesday, July 13, 2011

Unfortunately, here in the Sonoran Desert of southern Arizona, there is not a great diversity of ichneumon wasps, at least not the larger, more colorful species that one finds routinely in the deciduous forests of eastern North America. I was delighted to find a female specimen of Therion morio at the Vernon Wildlife Area near Mukwonago, Wisconsin on June 25. Even more amazing, it actually paused long enough for me to snap a few images. The one below is the best of the lot in the dim light of the forest understory.

This species is about the size of a black and yellow mud dauber, and it would not be surprising to find it is indeed a mimic of Sceliphron caementarium. The rule of thumb with ichneumon wasps is that if it looks like a stinger, then it isn’t a stinger. Such is the case here. The female has a short, spine-like egg-laying organ called an ovipositor. She does not use it in self-defense, only to inject eggs into caterpillars.

The larvae of this wasp are internal parasites of moth caterpillars, including the Fall Webworm, Hyphantria cunea, so this ichneumon should be considered a beneficial biological control of such pests. Other recorded hosts include the larvae of other tiger moths (family Arctiidae): Cycnia inopinatus; the Virginia Tiger Moth, Spilosoma virginica; the Saltmarsh Caterpillar, Estigmene acrea; and the Spotted Tiger Moth, Lophocampa maculata. While the wasp’s egg is laid in a caterpillar host, the adult offspring will emerge from the moth’s pupal stage.

Therion morio, which has no common English name, is a widespread species ranging from Nova Scotia south to Florida and west to Washington, northwest Nevada, southeast Kansas, and Mexico.

Sunday, July 10, 2011

You would think that by virtue of the fact that spiders are venomous they have few enemies willing to tangle with them. Such is not the case. Some spiders have therefore evolved to look like other animals that are even more distasteful or hazardous to potential predators. Many spiders resemble ants, for example, and one common example is the Twobanded Antmimic, Castianeira cingulata.

The only reason I was able to get clear images of this particular female specimen was because she had climbed to the top of a doorknob and seemed perplexed as to where to go next. She actually “danced” in place, raising her abdomen and making choreographed movements with her legs. While antmimic spiders in the family Corinnidae are adept hunters, they do not see quite as well as wolf spiders and jumping spiders. I am not sure whether she detected my presence or not, though it seems likely that she did.

At only 7-8 mm in body length for females, and 6-7 mm for males, these are not imposing creatures. Their size does match that of carpenter ants, though, and so does their coloring and overall body shape. The two pale bands on the abdomen may serve to give the impression that there are actually three body segments instead of two. Even more astonishing is that the spiders behave like ants, even appearing in the company of ants to reinforce their disguise. They move reasonably slowly when prowling, bobbing their abdomens and even waving their front legs like a pair of antennae.

Why bother mimicking ants? Carpenter ants in particular are pugnacious creatures that can bite fiercely and also emit formic acid, a very repulsive chemical compound. Few other insects, or spiders and other predators want to take on such an aggressive dynamo, so looking and acting like an ant has its advantages.

Castianeira cingulata ranges from the northeastern U.S. and adjacent southern Canada east to South Dakota and south to Arkansas and Florida. It inhabits woodland habitats, scouring the leaf litter on the forest floor for insect prey. The spiders are active both day and night. The spiders can overwinter in dense silken sacks that they spin in sheltered situations such as rock crevices and the recesses of decaying logs. It is suspected that they can potentially live several years, at least in the southern reaches of their range.

Saturday, July 9, 2011

Perhaps no insects embody “beauty and the beast” better than the green lacewings of the family Chrysopidae. The average person would be hard-pressed to make the connection between the hideous larva and the delicate adult it is destined to become. Who could blame them? Gardeners might easily mistake the sickle-jawed immature stage as a villain rather than a hero.

The family name Chrysopidae translates to “gold eye,” and indeed the adults of some species of green lacewings have eyes that seem to have fallen out of a kaleidoscope. The family belongs to the insect order Neuroptera or “nerve-winged insects.” This name comes from the dendritic pattern of wing venation and is not to imply that the wings of these insects feel any kind of sensation, at least any more so than in any other insect.

There are fourteen genera and at least 85 species of green lacewings occurring in North America. No doubt more species await description by scientists. These are very abundant animals, and just about everyone, from city center to rural countryside, has had an adult green lacewing or two (or several) visit their porch light at night. What can easily escape attention, however, are the other stages in the life cycle of chrysopids.

Let’s start with the egg stage. Believe it or not, the little white balls on the ends of these hairlike stalks are lacewing eggs. One could mistake the egg clusters for the fruiting bodies of some kind of fungus, and when they appear on a leaf or stem, cause a gardener some degree of concern. The female lays her eggs on these stalks for good reason: to keep them out of reach of predators like….well, her offspring’s siblings for example. So voracious are larval lacewings that they will not hesitate to cannibalize a brother or sister right off the bat.

Larval lacewings are undeniably ugly: worm-like bodies studded in clusters of spines, with a head dominated by jaws that look like ice block tongs. As if they are aware of their own ugliness, the larvae of some species conceal themselves under a layer of debris that they stick on those clusters of spines along their backs. What goes into this “garbage pile” might include bits of lichen, dust, or even the bodies of their victims. The real reason the larvae disguise themselves is not to redeem their ugly appearance, of course, but to make them appear innocuous to their prey and hide them from their own predators.

Lacewing larvae prey mostly on aphids, which has earned them the nickname “aphidlions.” They won’t pass up the opportunity to kill a caterpillar or other insect, either. They simply approach a prey insect and grab it with their jaws. Puncturing the body of their prey, they inject fast-acting paralytic compounds and digestive enzymes that go to work immediately on the victim, essentially liquefying its internal organs and tissues. The aphidlion then draws out a fluid meal, also through its hollow jaws.

Aphidlions are themselves vulnerable to various predators, namely the ants that guard colonies of aphids. Aphids secrete a sweet, liquid waste product called honeydew, and this is highly coveted by ants. The ants therefore vigorously defend the aphids from their predators and parasites. So, those lacewing larvae hidden under a blanket of debris might more easily escape detection by ants than a naked aphidlion would.

Once it emerges from the egg, an aphidlion proceeds through only three instars (intervals between molts). A mature larva will then spin an opaque, silken cocoon before transforming into the pupal stage. The mature adult will chew its way out of the cocoon, leaving the empty vessel looking like a tin can with the lid hanging by a hinge of remaining metal.

The adult insect is delicate-looking but durable, and highly colorful. They find mates by a kind of Morse Code, drumming their abdomens in a species-specific rhythmic pattern that the opposite gender recognizes. So precise is this courtship “song” that some species can be separated only by differences in their tune. The species themselves are physically identical. The adults do feed. Some continue their predaceous lifestyle, but others feed on aphid honeydew, or nectar or pollen.

Green lacewings are best appreciated as living creatures. The color of their bodies and eyes quickly fades after death. Be on the lookout for the larvae, but be careful. There have been reports of bites from larvae that fall out of trees and onto people, with reactions to bites varying from a nuisance to extremely painful with relatively persistent effects. Mostly, lacewing larvae should be considered among your best friends when it comes to waging war on garden and crop pests.

Wednesday, July 6, 2011

The Fourth of July holiday here in the United States celebrates our successful declaration of independence from British rule. Who would have thought that a bunch of settlers could pull that off? Well, the tradition continues as other European species continue to establish themselves on American soil. One of the most successful has been Polistes dominula, known here as the European paper wasp.

Note that this species has also been known as Polistes dominulus, but that name was a violation of Latin “gender” rules according to the International Commission on Zoological Nomenclature. No, there really is such an organization. I don’t fully understand the change, either, but I acknowledge that the Kaufman Field Guide to Insects of North America is in error. My bad, to be corrected whenever we are directed to turn out a revised edition.

The first observation of P. dominula in North America was made by G. C. Eickwort near Boston, Massachusetts in 1978. It is native to Eurasia, occurring over most of central and southern Europe, east to China and south to northern Africa and the Middle East. It therefore has a long history of living alongside people, and that affiliation is reflected in the largely urban distribution of the species here in the states. My own experience while collecting in Cincinnati was shocking. The European Paper Wasp went from an uncommon novelty in 1994 to probably the dominant species of Polistes by 1998. Now this species is known from most states and southern Canada, except for much of the Great Plains and Prairie Provinces (and apparently the Appalachian region as well).

Paper wasps are social, forming relatively small colonies. They build exposed combs from woody fibers they chew into a durable papery material. While the European Paper Wasp seems to prefer to nest in cavities (making them an enemy to those who put out bird boxes and check them), the species will also nest under the eaves of buildings and even among the tangled branches of shrubs. Nests peak at only a few dozen individual wasps, usually in late autumn.

Polistes dominula is rather small for a paper wasp, with a forewing length measuring 9-13 mm. Its compact body, relatively short legs, and bold black and yellow color pattern has contributed to it being mistaken for one of the yellowjackets, a different kind of social wasp in the same family, Vespidae. The orange antennae of P. dominula help one to identify the species with ease. No other social wasp in North America has orange antennae.

Like other paper wasps, the European Paper Wasp feeds its larval offspring pulverized caterpillars. The adult “worker” wasps are very efficient hunters, and there has been worry that some of our native butterfly and moth species may suffer from this new predatory pressure. The flip-side of that concern is that garden pests like cutworms and armyworms are probably being suppressed by the added predator species. P. dominula will take other insect prey, too, which allows it to be even more successful than our caterpillar-focused native species.

Adult wasps can be found nectaring on flowers, especially grape and other umbelliferous blossoms. The wasp above, imaged on the campus of the University of Massachusetts (Amherst) was chasing off all other insects attempting to visit the flower it was stationed at. This species can also damage ripening grapes in vineyards, and cherries in orchards (at least in western Colorado). Paper wasps are also very fond of “honeydew,” the sweet liquid waste products produced by aphids, scale insects, and related true bugs.

This wasp has been studied intently, and one headline-making investigation demonstrated that female dominance hierarchy in a given colony is predicated on the facial markings of the individual wasps. This does not necessarily correspond to overall fitness, though larger specimens tend to overwinter more successfully.

Only the female paper wasps survive the winter, tucked into insulated crevices where they achieve a state of lowered metabolism known as “torpor.” They then emerge the following spring to found or co-found new nests. Ultimately, only one female will lay eggs in the nest, even if another female cooperated in building the nest.

Interestingly, while most of our native paper wasp species are plagued by stylopids, the “twisted-wing insects” of the order Strepsiptera, P. dominula appears to be immune to these parasites, or nearly so. Paper wasps with what appear to be seeds wedged between abdominal segments are victims of stylopids.

Sunday, July 3, 2011

Cellar spiders are named for their habit of building their webs in cool, dark places such as basements, old mine shafts, wells and the like. Indeed, many members of the family Pholcidae do frequent such situations. However, this is not true of the Marbled Cellar Spider, Holocnemus pluchei.

The Marbled Cellar spider is actually native to the Mediterranean region of Europe. The earliest known record in North America comes from Sutter County, California in 1974. Because this species closely resembles the common Long-bodied Cellar Spider, Pholcus phalangioides, it is possible that it became established prior to 1974. The current U.S. distribution of the Marbled Cellar Spider ranges east to at least central Texas, and north to southern Oregon.

I find this species to be far more common outdoors than I do indoors here in southern Arizona. The webs of Holocnemus are irregular but decidedly dome-like, at least when one individual spider is off by itself. This is rarely the case, though, and many specimens will together form nearly contiguous webs that stretch far and wide. Dr. Elizabeth Jakob of the University of Massachusetts (Amherst) has found that up to fifteen individual spiders may share a communal web at any one time, with “membership” changing periodically. The spiders do compete over prey items, but skirmishes are rarely protracted.

Nearly any building overhang or dense tangle of vegetation will do for a web location. The primary criterion seems to be that the spiders do need shade from the unrelenting sun. At the Tucson Botanical Gardens I find a favorite place for this species to build its webs is among the leathery, spine-studded leaves of agave plants. Not many enemies of these spiders want to pursue them among the botanical equivalent of barbed wire.

The body length of mature female Holocnemus pluchei spiders is only 6-8 millimeters (males 5-7 mm, see image above), but their long, sprawling legs make them appear much larger. While this species is not regarded as dangerously venomous to people or pets in terms of the virulence of its venom, it has recently been discovered to have allergenic properties. According to this article, the species produces arginine kinase, a newly-described asthma-inducing allergen.

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Eric R. Eaton

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